Django-跨请求在表单数据中携带文件

Question

我有一个具有以下格式的模板：

<form enctype="multipart/form-data" action="{% url 'ngnmgmt_import_metro_area' %}" method="post" class="tds_form" id="import_metro_area_form">
  {% csrf_token %}
  <h3>Metro Area File Upload</h3>
  <div class="form-group">
    <!-- Would like to somehow re-attach my file here if it exists -->
    <label for="metro_area_file_upload">Select a Metro Area file to import.</label>
    <input id="metro_area_file_upload" name="metro_area_file" type="file">
    <!-- Alternatively, I would be happy to put the file in a hidden input or
         pass the file some other way, and hide the above input -->
  </div>
  <div class="row">
    <button class="btn btn-primary" type="submit">Check for Existing Items</button>
    {% if view_changes %}
    <button class="btn btn-success" type="submit" name="load_changes" value="True">Import Metro Area</button>
    {% endif %}
  </div>
</form>

和类似以下内容的视图：

class ImportMetroArea(LoginRequiredMixin, PermissionRequiredMixin, TemplateView):
    template_name = 'ngnmgmt/import_metro_area.html'
    login_url = '/login/'
    permission_required = 'commons.change_metroarea'

    def __init__(self, **kwargs):
        super(ImportMetroArea, self).__init__(**kwargs)
        self.load_changes = False
        self.view_changes = False

    def get_context_data(self, **kwargs):
        context = {
            # I would like to pass the file back
            # through the context, and somehow re-attach it
            # to my form file input
            "file": self.file,
            "load_changes": self.load_changes,
            "view_changes": self.view_changes,
            # Other irrelevant context data...
        }

        return context


    def get(self, request, *args, **kwargs):
        context = self.get_context_data()
        return render(request, self.template_name, context=context)

    def post(self, request, *args, **kwargs):
        self.load_changes = request.POST.get("load_changes")
        self.file = request.FILES.get("metro_area_file")

        if not self.load_changes:
            self.view_changes = True

        if not self.file:
            context = {
                "errors": ['Please upload a file.', ]
            }
            return render(request, self.template_name, context=context)

        // Do stuff that happens whether we are loading changes or not

        if self.load_changes:
            // Actually load the changes

        context = self.get_context_data()
        return render(request, self.template_name, context=context)

基本上，这是一个两步过程，在第一个POST中，我们确定要更改的内容，在第二个POST请求中，我们实际加载更改。

当前，在第二步中，用户必须将相同文件重新附加到文件上传表单。我希望将此文件保留下来并在第二步中重新附加。